As features on microelectronic circuits become smaller and as device speeds increase, we have been fast approaching the limits inherent in the electrical communication of signals. The capacitances in the microelectronic circuits along the electrical connections cause delays that cannot be ignored. More and more sophisticated techniques have been required to circumvent or push back these limitations. One direction in which people have turned their efforts has been to use photons instead of electrons to communicate information. Optical signals are not affected by capacitance, inductance, and ohmic resistance that are present in the circuit elements and photons travel much faster than the electrons. As a consequence, in recent years there have been many advances in the field of optical communication and processing of signals and in optical media and devices that enable optical communication and processing.
These efforts have also had their impact on the integrated circuit fabrication industry as more people search for ways to combine or integrate photonic elements with the microelectronic devices that have been fabricated on IC chips. There have been many recent advances involving the fabrication of optical waveguide structures on silicon substrates, the fabrication of photodetectors to convert the light to electrical signals that can be used by conventional microelectronic circuitry and the fabrication of light emitters or laser elements for converting the electrical signals to optical signals.